1. Field of the Invention
The invention relates to a method of detecting the speed in an internal combustion engine, in which method a sector wheel connected to a crankshaft is scanned and the time taken for a sector of a certain size to pass is determined.
2. Description of the Prior Art
Such speed detection methods are conventional in internal combustion engines, in which case a gear with 60 teeth which is attached to a crankshaft is normally scanned. Since, as a result of the working principle of an internal combustion engine with constant change between compression and expansion of the working gas, the speed is not constant but has a periodic oscillation superimposed on it, this periodic oscillation originating from different torque contributions of the individual cylinders, averaging is normally carried out during the speed detection to the effect that several teeth of the gear are scanned. As a rule, the scanning is effected over an angle of rotation of the crankshaft of 180°, which corresponds to a working stroke of a four-cylinder four-stroke internal combustion engine. The scanning of shorter sectors or of a smaller number of teeth would entail too large an error on account of the abovementioned periodic oscillations.
In modern control units of an internal combustion engine, the averaging effected by the scanning of several teeth may be selected in virtually any desired manner with regard to the start of averaging or the end of averaging. Before certain control actions, for example the injection of fuel into cylinders of a diesel internal combustion engine, the averaging is started with respect to time in such a way that it is completed immediately before the planned action in order to than have speed information which is as current as possible. However, on account of the averaging over a working stroke, i.e. an angle of rotation of the crankshaft of 180°, the speed information is nonetheless not as current as would actually be desired, since averaging, from the communication point of view, constitutes a filter with low-pass function.